Small-interfering RNA (siRNA)-mediated silencing of genes offers a novel approach for disease treatment. Direct delivery of siRNA to respiratory epithelia is potentially advantageous for many respiratory infections and for chronic diseases like cystic fibrosis where airway epithelial cells are prominent sites of production and release of pro-inflammatory cytokines such as IL-8 and others (Davidson B L, McCray P B, Jr. Current prospects for RNA interference-based therapies. Nat Rev Genet 2011; 12(5):329-340). Topical delivery avoids hepatic clearance and non-specific accumulation associated with the systemic route and allows for local accumulation within the target organ. But due to its high molecular weight and polyanionic nature, siRNAs do not cross the epithelial cell membrane freely. In addition, the intra pulmonary physical barriers such as mucus to overcome before encountering the problems with cell entry (Oakland M, Sinn P L, McCray P B Jr. Advances in cell and gene-based therapies for cystic fibrosis lung disease. Mol Ther. 2012 Feb. 28. doi: 10.1038/mt.2012.32. [Epub ahead of print] PMID: 22371844). Thus, efficient delivery of siRNA to the airways has been challenging due to significant intracellular and extracellular barriers.
Non-viral siRNA delivery is an attractive and potentially safer alternative to virus-based delivery systems. A number of studies report successful delivery of naked siRNA to airways, especially for counteracting viral infections (Zhang W et al., Inhibition of respiratory syncytial virus infection with intranasal siRNA nanoparticles targeting the viral NS1 gene. Nat Med 2005; 11(1):56-62; Bitko V et al., Inhibition of respiratory viruses by nasally administered siRNA. Nat Med 2005; 11(1):50-55). However, recent reports also show that siRNAs delivered intranasally or intratracheally, without delivery enhancement, may not target to lung cells and thus do not cause RNA interference (Moschos S A et al., Uptake, efficacy, and systemic distribution of naked, inhaled short interfering RNA (siRNA) and locked nucleic acid (LNA) antisense. Mol Ther 2011; 19(12):2163-2168). Furthermore, off target immunostimulatory effects of early siRNA constructs likely clouded some studies (Judge A D et al., Sequence-dependent stimulation of the mammalian innate immune response by synthetic siRNA. Nat Biotechnol 2005; 23(4):457-462; DeVincenzo J et al., A randomized, double-blind, placebo-controlled study of an RNAi-based therapy directed against respiratory syncytial virus. Proc Natl Acad Sci USA 2010; 107(19):8800-8805; Kleinman M E et al., Sequence- and target-independent angiogenesis suppression by siRNA via TLR3. Nature 2008; 452 (7187):591-597). Added to these disappointing results, the delivery and efficacy of siRNA in combination with various non-viral reagents in respiratory epithelia has not been extensively investigated.
Accordingly, a more effective, simple-to-administer, and efficient treatment for airway epithelial disease is needed.